Cellular communication systems are comprised of cells. Each cell in a cellular communication system may be controlled by a base station or access point device, wherein a base station may be arranged to control more than one cell, for example where cells are formed as directional sectors or where cells are configured to operate on different frequencies.
When mobile terminals roam in a coverage area of a cellular communication system, they may move from a coverage area of a first cell to a coverage area of a second cell. To maintain connectivity toward the communication system, the serving cell of such a terminal may be reassigned from the first cell to the second cell. The mobile terminal may periodically measure for signals transmitted from the first and second cells to find out, when a handover from the first cell to the second cell is useful. For example, when the mobile terminal detects that a signal strength of a signal transmitted from the first cell declines while a signal strength of a signal transmitted from the second cell increases, the terminal may conclude it is moving toward the second cell.
When a cellular communication system comprises cells operating on frequencies not very close to each other, measuring for signals transmitted from cells operating on different frequencies than the serving cell may be difficult for the mobile terminal. For example, when the second cell operates on a different carrier frequency, it may be necessary for a mobile to re-tune its radio receiver to measure a signal transmitted from the second cell. Such a measurement may be referred to as an inter-frequency measurement. In these cases, once a mobile terminal discovers a cell operating on such a different frequency, it may store data relating to the radio environment prevailing on the frequency of the originally serving cell. When the mobile terminal is again in the same place, it may determine from the stored data that the radio environment on the frequency of the serving cell is similar to what it was when previously a cell operating on a different frequency was found. The terminal may report this to a base station controlling the serving cell, responsive to which the serving cell may instruct the terminal to perform an inter-frequency measurement. Such data relating to the radio environment may be referred to as a radio fingerprint.
Heterogeneous cellular communication networks comprise cells of more than one type, for example macrocells to provide wide-area coverage, and small cells to provide high capacity in areas with high demand for network service. In heterogeneous networks, small cells may be configured to be controllable by macrocells, wherein the network may have a hierarchical structure.